1. Field of the Invention
The present invention relates to an optical disc recording device and an optical disc recording method for recording data in an optical disc storage medium. In particular, the present invention relates to an optical disc recording device and an optical disc recording method for recording data in DVD-RW or DVD+RW.
2. Description of Related Art
The optical disc recording device such as a DVD recorder or a BD recorder records data in an optical disc such as a DVD or a BD using a laser beam emitted from a semiconductor laser element mounted on an optical pick-up. In this optical disc recording device, electric drive power of the laser beam is determined in accordance with a type of the optical disc.
For instance, the electric drive power for recording data in DVD-RW or DVD+RW is constituted of a bottom electric power for driving the semiconductor laser element to emit light with an optical output of bottom power Pb, an erase electric power for driving the semiconductor laser element to emit light with an optical output of erase power Pe, and a peak electric power for driving the semiconductor laser element to emit light with an optical output of peak power Pw. These electric powers are set to predetermined values. In addition, these electric powers are usually controlled by drive current Iop of the semiconductor laser element. FIG. 6 is a graph illustrating optical output characteristic of the semiconductor laser element to the drive current in a conventional example. As illustrated in FIG. 6, the bottom power Pb is controlled by bottom current (current value Iread). In addition, the erase power Pe is controlled by erase current (current value Ie). In addition, the peak power Pw is controlled by peak current (current value Iw).
When data is recorded in DVD-RW or DVD+RW, a current value of a bottom current Iread1 and a current value of an erase current Ie1 are set based on L1 in FIG. 6, for example, before a recording operation is started. Then, based on the current values Iread1 and Ie1, a current value of a peak current Iw1 is set. The current value of the peak current Iw1 is set so that a ratio of a difference between the current value of the erase current Ie1 and the current value of the bottom current Iread1 (Ie1−Iread1) to a difference between the current value of the peak current Iw1 and the current value of the bottom current Iread1 (Iw1−Iread1) becomes a predetermined ratio ε (ε>1), as described in JP-A-2009-245487, JP-A-2004-342271, JP-A-2004-326841, JP-A-2009-87399, and JP-A-2004-199839, for example.
The determined current value of the bottom current Iread is not changed until a recording process is finished, but the current value of the erase current Ie1 is feedback controlled so that the erase power Pe does not change during the recording operation. In addition, the current value of the peak current Iw1 is controlled as described above in accordance with the current value of the bottom current Iread1 set before starting the recording operation, the current value of the erase current Ie1 that is feedback controlled, and the predetermined ratio ε.
However, data is recorded by one recording operation in DVD-RW or DVD+RW. Therefore, if the data length is long, element temperature of the semiconductor laser element during the recording operation may be raised so that the optical output characteristic of the semiconductor laser element to the electric drive power (particularly to the drive current Iop) may change. In this case, because the optical output of the semiconductor laser element varies during the recording operation, the recording operation may not be performed appropriately, so that the recording process may not be continued, or data recorded in the recording operation may not be read out.
For instance, in FIG. 6, if the element temperature is raised during the recording operation so that the optical output characteristic of the semiconductor laser element changes from L1 to L2, the current value of the bottom current Iread necessary for optical output of the laser beam with the bottom power Pb changes. In this case, the erase power Pe is not changed because it is feedback controlled in accordance with the optical output of the laser beam, the erase current Ie necessary for optical output with the erase power Pe changes from Ie1 to Ie2. Therefore, the current value changes by ΔIe based on the characteristic curve L2. On the other hand, the peak current I also changes from Iw1 to Iw2, but the current value of the peak current Iw is set to a vale after changing by (ε·ΔIe) in accordance with the variation ΔIe of the current value of the erase current Ie. Therefore, the optical output of the semiconductor laser element (light emission power) changes from the peak power Pw by ΔP.
In contrast, in JP-A-2009-245487, the ratio ε is corrected based on a sensitivity coefficient indicating a relationship between a monitor value of the laser beam emitted from the semiconductor laser element and the electric drive power, so that the variation of the electric drive power is suppressed. In addition, in JP-A-2004-342271, an average value of the light emission power of the semiconductor laser element is determined, which is sample-held during a light emission period with the current value of the erase current. Then, using the determined average value and the current value of the erase current, the current value of the peak current for obtaining the peak power for recording data is determined from a ratio between a current value and a light emission power of the semiconductor laser element. In addition, in JP-A-2004-326841, amplitude of a pulse waveform of a control signal changing between a current value at the bottom power and a current value at the erase power is measured in states where the semiconductor laser element is driven to emit light with the bottom power and with the erase power. Then, the current value of the peak current is determined based on the current value of the erase current determined from the amplitude and the value ε determined from a recording speed. In addition, in JP-A-2009-87399, an ideal current value of the erase current is determined from an erasing ratio when the current value of the erase current is changed. Then, the current value of the peak current is determined from the ideal current value of the erase current and the ratio ε. In addition, in JP-A-2004-199839, a variation of the current value of the erase current is added to or subtracted from the current value of the peak current so that the current value of the peak current is maintained to be constant. However, in JP-A-2009-245487, JP-A-2004-342271, JP-A-2004-326841, and JP-A-2009-87399, it is necessary to monitor a light emission power of the laser beam, an erasing ratio of DC erasing, a pulse waveform of the control signal, so as to perform the feedback control. In addition, in JP-A-2004-199839, an adding circuit or a subtracting circuit is necessary. Therefore, there is a problem that the device structure becomes complicated, and manufacturing cost is increased.